This invention relates to a magnetically activated circuit-breaker device, and more particularly, to the magnetic armature for such a device.
U.S. Pat. No. 4,479,101 has for its subject an electrical circuit breaker having an automatically adjusting magnetic armature. FIG. 1 is a side view of the circuit breaker of U.S. Pat. No. 4,479,101 with its side cover removed. In general, this type of circuit breaker operates in two different modes to open the contacts. In both modes an armature 10 having a latch holder 12 is moved downward such that the interference between the latch holder 12 and the end 14 of the cradle 16 ceases and the contacts 18 are caused to separate. FIG. 2 illustrates the armature 10 of U.S. Pat. No. 4,479,101.
The distinction between the contact opening modes involves the manner in which the armature is moved downward. In the first mode, the armature 10 is urged downward by a magnetic force produced by the magnetic yoke 18 when the current flowing through the circuit breaker exceeds a predetermined amount. In the second mode, the armature 10 is urged downward by a bimetallic strip 20 which is in contact with the end hook extension 22 of the armature 10. When the current flowing through the bimetallic strip 20 reaches a predetermined level, the end portion of the bimetallic strip 20 moves downward due to heating and contacts the hook extension 22 causing the armature 10 to move downward.
FIG. 3 illustrates an enlarged view of the interface between the latch holder 12 and the end 14 and the engagement length X of the interface between the latch holder 12 and end 14. The length X determines the distance the armature must travel before the interference between the end 14 and the latch holder 12 ceases causing the contacts 48 to open. Additionally, it is advantageous to accurately maintain the predetermined length X for all circuit breakers of a given model and rating. Accurately maintaining the length X provides better consistency for purposes of calibration.
Referring to line A--A in FIG. 1, an air gap distance is defined along line A--A between the top of the magnetic yoke 18 and the bottom of the armature 10. This distance affects the time it takes for armature 10 to be urged downward when there is a fault current in the circuit breaker.
Accordingly, it would be useful to provide a simple and inexpensive means for providing a consistent distance X and/or reducing the air gap distance. Additionally, it would advantageous to provide a means for performing this task without requiring extensive modification of the circuit breaker housing and the circuit breaker components, since these modifications would most likely render certain existing tooling and manufacturing processes useless.